1. Field of the Invention
The present invention relates to an image display system, and more particularly to an image display system suitable for performing a signal processing of a color image data using a compressed data.
2. Description of the Related Art
Conventionally, at a time when transmitting/receiving a color image, for example, it is adopted a system of setting up a screen on which a plurality of pixels are arranged, of defining a scanning system of pixels that constitute the screen, as well as of sequentially transmitting color image data with respect to each pixel based on this scanning procedure, for a television transmitter, and of displaying the received color image data in a defined scanning order, on a receiver side. For example, a CRT (Cathode Ray Tube) is configured to perform a display for each pixel by projecting an electron beam that is narrowly focused, onto a surface of a fluorescent material, and then to display a color image over an entire screen by scanning the electron beam. In this case, in high vision broadcasting for a purpose of an enhancement of an image quality, the number of pixels that constitute the screen has been increased comparing to the conventional television broadcasting. Further, in a display device that is used in a computer terminal and the like, at a time when enhancing a quality of an image, it is adopted a system of increasing the number of rewritings (frame rates) of the display screen as well as an increase of the number of pixels.
On one hand, in a liquid crystal display device, a plasma display device and the like, it is adopted a structure (configuration) of constituting a pixel that becomes a unit of a display as a circuit-like, and of displaying a color image on a screen, by supplying a display signal to each pixel while selecting each pixel. In this kind of display device, it is constituted to display a color image by inputting data with respect to a color image through a wire from a display control device that creates or stores a display data, supplying the inputted data to each pixel using a driver circuit, and then driving each pixel sequentially. In this case, as a method of enhancing a quality of an image to be displayed, increasing the number of pixels within the screen and/or of increasing the frame rate are/is adopted.
Incidentally, in-order to enhance an image quality, if the number of pixels and the frame rate are increased, and thus a capacity of the image data increases, so that, as a method of decreasing the capacity of the image data, it has been proposed a compression system that utilizes a characteristic of an image signal. As one example, in a still-picture, the JPEG (Joint Photographic Expert Group), and in animation, the MPEG (Motion Photographic Expert Group) and the like have been widely adopted. These systems implement a compression processing of a block in which a plurality of pixels are combined as a unit, and for the JPEG, the amount of data of the original picture (image) can be compressed to the degrees of 1/10 to 1/20. As described above, even if it is a case of implementing a data transfer with a limited transmission capacity, by compressing the data, increasing the number of pixels and the frame rate can enhance the image quality.
In general, enhancing an image quality is equivalent to increasing an amount of information to be sensed visually, and this is eventually equivalent to increasing an amount of data to be displayed. As a result, an enhancement of an image quality can be planned, by simply increasing the number of pixels that constitute the screen, or increasing the number of rewritings (the frame rate “f”) of the display screen, as in the conventional technology. However, for an increase of the amount of data, it is not possible to increase the number of pixels and the frame rate all together under a certain processing capability.
That is, assuming that a processing time for a sheet of screen is “pf”, a time required for a generation or an input of a display data is “pi”, and a transfer time of the display data is “pt”, then a processing time for the sheet of screen “pf” is expressed as pf=pi+pt. Herein, if the processing time “pf” for the sheet of screen is proportional to the number of pixels, then increasing the number of pixels for the purpose of an enhancement of the image quality causes the processing time “pf” to be extended, and eventually this causes the frame rate “f” to be decreased. That is, if the processing time “pf” for the sheet of screen is a constant (the data generation processing capability=k pixel/sec.), or if the display capability is a constant, the display capability is in a relationship of the display capability=the number of pixels×the frame rate, and thus two parameters such as the number of pixels and the frame rate are in the inversely proportional relationship. In other words, for the increase of the amount of data in the image data, it is not possible to increase two parameters of the number of pixels and the frame rate simultaneously, under a certain device capability.
For example, a so-called VGA screen is constituted of 640 horizontal pixels and 480 vertical pixels, and a so-called UXGA screen is constituted of 3200 horizontal pixels and 2400 vertical pixels, and the ratio of the number of pixels between two screens is 1:25. Further, in the common television broadcasting, a screen of 30 frames per second is transmitted for reproducing and displaying the motion pictures, and on one hand, for a screen display of a computer terminal and the like, a high frame rate such as 120 frame per second is set up, for example, and the ratio between the frame rates in both cases is 1:4.
Now, considering the case that the image data by the VGA screen is transferred in 30 frames/second, and the image data by the QUXGA screen is transferred in 120 frames/second, an amount of data for a display is a multiplication of the frame rate and the number of pixels, and the ratio of the amount of data in both cases is 1:100. Accordingly, if there is no restriction in a data transfer path, at a time when the amount of data increases along with the increase in the data generation capability, the increased data can be easily transferred, if the frame rate is made to be higher, but if the transfer condition of the data transfer path is 30 frames/second, then for transferring the data corresponding to 120 frames/second, the amount of data transfer is restricted by the transfer condition, and thus it can not be dealt with the increase of the amount of data.
As described above, if the processing time “pf” or the display capability for the sheet of screen is a constant, it is not possible to increase the number of pixels and the frame rate simultaneously, along with the increase of the amount of data.
Further, a processing time largely depends on a capability of a device that performs a screen display, and thus it is possible that the device for generating the data and the device for receiving the data have the different capabilities. For example, if a generation capability of a display data is equivalent to the one of television broadcasting, when the display device has the ability of the QUXGA, then an image that can be displayed in practice is equivalent to the one of the television broadcasting. Conversely, even if the processing time “pf” is shortened by increasing the capability of the device that performs the processing, there is a case that an upper limit value of the frame rate “f” possessed by the display device becomes a restriction. As described above, at a time when processing the image data, if the capabilities of the device for generating the data and of the device for receiving the data are not managed, the capabilities of devices can not be utilized sufficiently as a whole system.